Venetian blind is widely welcomed by consumers and has gradually taken the place of conventional cloth curtains in the market due to the convenient operation, angle-adjustable strips, and low cost of the venetian blind. A new type of venetian blind formed from cloth-made strips has developed considerable potential in the market. Such cloth strips are usually provided with side ribs to increase their rigidity. The present invention relates to an apparatus for automatically ribbing the cloth strips of a venetian blind, so that such cloth venetian blind strips can be ribbed in an accurate, efficient, and mass production manner.